Browsing by Author "Davis, Brian K."

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    Chromosome identification and analysis in selected lines of laboratory mice
    Schmitt, Athanasia Nancy Panos (Virginia Tech, 1976-06-05)
    Chromosome preparations from 102 ICR albino mice were examined using a modified trypsin Giemsa staining technique. The mice were from four lines selected for maximum rate of post-weaning gain (28 generations), one line selected for minimum rate of post-weaning gain (25 generations), and two unselected control lines. Mitotic metaphase chromosome preparations were obtained from bone marrow cells of adult male and female mice. Two similar treatments were utilized in obtaining the chromosome preparations. The first treatment consisted of: 50 minute colchicine pretreatment, 30 minute hypotionic pretreatment, four-glacial acetic acid-methnanol fixation periods, 15 second trypsin period and 15 minute Giemsa staining period. The second treatment varied from the first, basically, in the length of hypotonic pretreatment, and length and number of fixation periods. A mean number of 40 telocentric chromosomes with very similar banding patterns was observed in all lines. Relative chromosome lengths for each chromosome were obtained. The lengths for the various lines, control, high and low, were compared by means of a pooled "t" test. Non-significant a₂ levels were obtained for the pairwise comparisons of the lines. Significant a₂ levels were obtained for the effects of the two treatments, trypsin and no trypsin. Karyotypes for each line were made with no chromosomal abnormalities detected in any of the lines. The selection regime followed has produced significant genetic change in several characteristics of these mice. However, these changes have apparently not been accompanied by observable alterations at the chromosomal level.
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    Human chromosomes: structure, abnormalities and birth defects
    Goradia, Ranjan Y. (Virginia Tech, 1977-08-05)
    The research presented in this dissertation consists of four papers that revolve around the structure of human chromosomes and their relationship to birth defects. A new technique is described to produce spiralization of human metaphase chromosomes. The important feature is heat followed by trypsin treatment. By varying conditions, it is possible to produce bands, spirals and intermediate states. An investigation of human metaphase chromosomes reveals identical lateral bands in sister chromatids when stained with Quinacrine mustard or Giemsa-trypsin. A hybrid of these two methods produces banding patterns which are different in sister chromatids yet may be repeated in homologous chromatids. A case study is presented in which a 3l-year old white female with a history of ovarian dysfunction and infertility delivered a male infant with trisomy 13. Her cultured leucocytes were mosaic for trisomy X. The natures of trisomy X and trisomy 13 are discussed with particular emphasis on the genetic transmission. In another case study of a family, it is found that some individuals who completely lack dermal ridges are mosaic for an extra X chromosome with deletions in both arms. A mechanism is proposed to account for the extra chromosome.